1. Field of the Invention
The invention relates to a reactor for use in water treatment and to micro film carriers for use in connection with the treatment, as well as to a method for operating the reactor. More specifically the invention relates to a reactor of the type in which the water is conveyed through the reactor which contains particle-like carriers on which a biofilm grows that generates the desired decomposition of the contamination.
2. The Prior Art
An example of such a reactor is described in Norwegian patent specification NO-B 172 687 in which the untreated water is introduced at the bottom of the reactor and at the water pressure in the inlet. The water rises up through the reactor and leaves through an outlet at the top. Due to the flow conditions the microfilm carriers will have a tendency to clot in the upper part of the reactor, and accordingly the reactor will not be so effective at the lower part.
In the reactor a biofilm is rapidly created on the plastic particles. On the outer surfaces the biofilm is abraded as the plastic particles rub against each other due to the flow in the reactor. On the exposed surfaces a continuous removal of dead microorganisms takes place such that the carriers always appear with a new active biofilm. It is different for the interior surfaces of the plastic particles; in the beginning the interior surfaces are active, but they rapidly become choked and can be completely sealed by dead biofilm, such that the interior surfaces rapidly become inactive. The dead biofilm leaves a black coating on the plastic particles which is difficult to remove. Among others this condition results in the fact that for the cylindrical plastic particles shown in FIG. 1 in the Norwegian patent specification one can only calculate with an effective surface of 57% of the total surfaces, thus approximately the same effectivity as for a solid plastic particle.
The phenomenon with dead biomaterial is especially critical for recirculated water for aqua cultures for which very strict requirements for the quality of the water are stipulated. Further, there is a requirement for a high degree of efficiency as it is necessary to place the plants indoors to avoid temperature fluctuation. Fish roe and fry require constant temperature conditions to develop at their optimum. Accordingly, the plants should be as compact as possible, such that the plants consume a minimum of space in the building.